The storage capacity of magnetic media can be increased by reducing the width and center-to-center spacing of the data tracks. As track densities increase beyond 1000 tracks per inch, the center-to-center spacing between tracks falls below 25.4 micrometers. Track width is determined by the shape and width of the poles of the writing transducer. The dominating factor is usually the width of the trailing pole as seen by the magnetic medium. Using current fabrication techniques, the bottom poles of write transducers are wider than the top poles. This asymmetry between the top and bottom poles cause the track widths to differ depending on the direction that the magnetic medium moves across the poles. Fabricating the top poles and bottom poles with the same width to eliminate directional track width dependencies is desirable. However, the photolithographic masks, wet etching, and/or de-plating techniques that are currently used to define the poles make this goal difficult to achieve.
"Tenting" also becomes more important as the width of the tracks decrease. Tenting occurs when debris lifts a flexible magnetic medium, such as magnetic tape, away from the tape bearing surface and the transducers. For example, a 1 micrometer debris particle 20 to 30 micrometers away from a write transducer may produce sufficient head/tape separation to cause a signal dropout during recording. Similar dropouts may occur while attempting to read in the presence of debris. Transverse slots are incorporated in some magnetic heads to remove air trapped between the media and the head, thereby keeping the head in close contact with the media. The transverse slots are found both upstream and downstream of the transducers to account for magnetic medium motion in either direction. Loose debris from the media tends to accumulate in these slots. Changes in the magnetic medium direction, excessive debris accumulated in the slots, the stop/start motion of the magnetic medium, or any other disturbance can cause debris to break loose from the slots. Debris ejected from an upstream slot may be swept across, or near the transducers potentially causing a momentary dropout.
Several groups are working to reduce the asymmetrical fringe fields caused by the asymmetrical top and bottom poles used in disk drive applications. In the articles "Recording Studies on Sub-Micron Write Heads by Focused Ion Beam Trimming", IEEE Transactions on Magnetics, Volume 33, No. 5, September 1997 by Gorman et al., and "Low Fringe-Field and Narrow-Track MR Heads", IEEE Transactions on Magnetics, Volume 33, No. 5, September 1997 by Guo et al., a focused ion beam is used to mill two channels that remove the sides of the top pole and form notches in the bottom pole. The effect of trimming the poles minimizes the side-fringing effects to minimize the erase width of the write transducers. These magnetic heads are intended for use in disk dive applications where the magnetic head sits inside a clean sealed environment and do not make contact with the magnetic disk. As a result, the channels disclosed in these articles do not address the need to minimize tenting induced by debris.